1. Field of the Invention
The present invention relates to the field of servicing boreholes which have been drilled by sidetracking a secondary wellpath, sometimes known as a lateral, from a primary borehole. More specifically, the present invention relates to servicing a desired lateral with a drilling, completion or workover tool assembly, commonly called a tool string, in a well from which multiple laterals may have been drilled.
2. Discussion of the Related Art
The purpose of drilling multiple laterals is to increase total reservoir drainage without incurring the cost of surface casing, surface site preparation and other expenses associated with drilling new wells originating at the earth's surface. Drilling these multiple laterals is known in the art. Multiple laterals are each drilled by re-entering the primary borehole and sidetracking. The primary borehole can either be an uncased or cased well. A lateral is usually drilled so that it is nearly normal to the primary borehole. The lateral is extended until it has achieved sufficient horizontal displacement for enabling the desired additional drainage in the target reservoir. In multiple lateral wells the primary borehole and the sidetracked laterals remain open after they are drilled. They are not plugged or otherwise obstructed, even at the portions of the primary borehole where the sidetracking process is begun, known as the kick-off-point.
Orienting a well drilling or completion tool string to enter a specific lateral in a multiple lateral well is known in the art. Drillpipe and workover tubing are normally used to convey the drilling or completion tools so that they can be oriented to enter the desired lateral. Rotational torque is applied to the drillpipe or tubing at the surface, turning the tool string to the proper orientation for entering the desired lateral, and a bent housing typically located near the bottom of the tool string assists in guiding the tool string into the lateral. However, use of bent housings for guiding drilling and completion tools into a desired lateral has drawbacks. Having sufficient bend angle in the housing to reliably guide the tool string into the lateral can cause difficulty in traversing the primary wellbore since the effective diameter of the tool string is increased by the axial displacement along the bend.
Drillpipe and tubing could also be used to convey an electric wireline tool string, such as production logging instruments or perforating guns, but drillpipe or tubing conveyance of wireline tools is time consuming and expensive. The drillpipe or tubing must be assembled into a continuous length by means of threaded couplings from sections whose length is normally thirty to ninety feet.
In the case of single wellbores without sidetracks, wireline or coiled tubing conveyance methods are commonly used with a high degree of success for running of wireline surveying, evaluation and completion tools. "World Oil's Coiled Tubing Handbook", Gulf Publishing Co., Houston, Tex. 1993, provides detailed descriptions of the use of coiled tubing to convey wireline tools into a single wellbore. With wireline or coiled tubing conveyed tools, however, it is not possible to apply rotational torque to the tool string from the surface. It is, therefore, difficult to orient the wireline tool string using the wireline or coiled tubing alone.